1. Field of the Invention
The present invention relates to a seat heater which may be used for e.g. heating of a vehicle seat, and a manufacturing method of the seat heater. More particularly, the present invention relates to a seat heater in which, a heating wire is provided on a base cloth, thereby the sufficient and stable adherent strength between the heating wire and the base cloth may be maintained for a long period of time, and in which a good seat feeling may be accomplished at a lower cost.
2. Description of the Related Art
There have been several conventional seat heaters, for example, a heater in which a winding (zig-zag) form of heating wire is placed on a sewable supporting body such as a cloth, so that the heating wire may be sewn and secured to the cloth by upper thread and lower thread (e.g. see a patent document 1), or a heater in which a winding (zig-zag) form of heating wire is placed on a supporting body such as a cloth, and is then caught and fixed between a pair of cloth sheets of which surfaces are coated with adhesive agents (e.g. see a patent document 2).
These seat heaters are actually used, for example by being inserted into a position between a seat pad and a surface cover of a vehicle seat.
Patent Document 1:
Official Gazette of Japanese Patent No. 2621437 (columns 4-6, FIG. 3); and
Patent Document 2:
Official Gazette of Japanese Examined Patent Publication No. Sho 63-19068 (column 3, FIG. 5).
In addition, although not prior arts directly relating to the seat heater, there are three cases which might have any relation as follows:
Patent Document 3:
Official Gazette of Japanese Examined Utility Model Publication No. Hei 6-25916;
Patent Document 4:
Official Gazette of Japanese Unexamined Patent Publication No. Hei 6-68964; and
Patent Document 5:
Official Gazette of Japanese Unexamined Patent Publication No. Hei 6-119967;
However, the above prior arts have the following disadvantages.
First, according to the structure in which the heating wire is sewn and fixed on the supporting body (i.e. the prior art as shown in the patent document 1), when a passenger sits on and leaves the seat, the application and the release of the load of the passenger shall repeatedly occur, thereby the thread might be loosened or cut, which would further result in a deviation of the heating wire inside the seat. When the heating wire is deviated from the regular position, there is a possibility that the seat may not be heated uniformly. This is very dangerous, since the deviated heating of the seat might cause the concentrated overheating of any part of the seat.
Thus, there have been several suggestions as the countermeasure therefor, for example to reduce the sewn pitch during fixing of the heating wire, or to fix the heating wire more tightly by increasing the sewing strength. However, in these cases, the supporting body must be made of any material having a sufficient thickness, and must also at least satisfy a required hardness.
However, when the above discussed supporting body is selected, there would arise another problem that the touch of the seat heater might become hardened, and thereby the seat feeling might become poor.
Further, as the fixing of the seat heater by sewing is very laborious, and the productivity is not good. Accordingly, there is another problem that the production cost would become higher.
On the other hand, according to the structure in which the heating wire is inserted and fixed in a position between the pair of cloth sheets with the adhesive agents thereon (i.e. the prior art as shown in the patent document 2), as the two supporting bodies must be used, and there exists the layer of the adhesive agent between these sheets, the touch might also become hardened, and the seat feeling might also become poor.
Further, this type of seat heater requires many component parts, and since the cloth sheet, of which surface being coated with the adhesive, is very expensive, the production cost would increase considerably.